1. Field of the Invention
This invention pertains to a method of vaccinating against infectious bursal disease (IBD) in chickens. More specifically, the invention comprises monoclonal antibodies specific to IBD virus (IBDV) which can be effectively employed in a vaccine to prevent the occurrence of this immunosuppressive disease.
2. Background of the Prior Art
Infectious bursal disease (IBD) has been identified as a significant economic drain in the poultry (chiefly, chicken) industry. IBD is caused by virulent field viruses which cause a highly contagious immunosuppressant disease condition, which exacerbates other infections in the chicken population. The disease has the greatest impact on young chickens, and is characterized by lesions in the lymphoidal follicles of the bursa of Fabricius.
As noted, it is particularly young chickens (less than three weeks old) that are most highly susceptible to the virus. These chickens are not yet totally immunologically competent. The conventional forms of treatment to prevent IBD include passive transfer of high levels of maternal antibodies against IBDV from breeder hens to their offspring which may provide temporary protection until the chicks become totally immunologically competent, or through inoculation of the young chicks with a virulent strains of IBDV.
Neither measure is entirely effective, because of the nature of the poultry industry. Specifically, poultry flocks tend to be large aggregations of young broilers obtained from a variety of widely dispersed breeder hen populations. As a result, immunity provided by either of the described methods tends to be both non-uniform, and often inadequate to resist the high challenge doses present in the field from other related strains of the IBDV which may differ from that employed in establishing initial immunity. This lack of uniformity of the level of protection is important because, when the chicks from different breeding groups or single, variable breeder flocks are mixed in a single poultry population, the chicks become susceptible to the effects of IBD at different times, where the level of protection is non-uniform. The result is that not only are some chicks still immune while others are susceptible to field infection, but the immune chicks will not subsequently become vaccinated with the avirulent strains that are normally given at around fourteen days of age. As a result, the chicks which were susceptible at time of vaccination become actively immune, those that were passively immune at the time of vaccination fail to become actively immune and, therefore, predictably, become infected with the field variety of IBDV as soon as maternal antibodies are used up or become critically low.
As is apparent, neither the passive immunization of chicks through the use of maternal antibodies, nor the active immunization achieved by inoculation with avirulent IBDV strains present, is adequate to provide significant protection to all poultry needed to overcome the economic loss represented by IBD.
Accordingly, a need to provide uniform, non-strain specific protection against IBD; specifically, immunity against IBD, without using live virus vaccines which may be adventitious remains a pressing need in the industry.